Devices used in the medical and dental industry are prepared from metals, ceramics, or synthetic or natural plastics and are often hydrophobic and non-slippery. Catheters and guide wires which are used for insertion through blood vessels, urethra or other body conduits require low-friction surfaces for preventing injury or inflammation of mucous membranes and for facilitating surgical procedures. To render the device more slippery, the device surfaces are often coated with low-friction materials, such as ptfe, Teflon.RTM., silicone oil, glycerin or silicone fluid. This low-friction coating may result in the loss of maneuverability of the device from outside the body because they are slippery even when dry. Surface modification of hydrophobic, non-biocompatible or non-slippery surfaces by coating with a hydrophilic polymer is known; however, hydrophilic polymer coatings, when hydrated, possesses little in the way of physical integrity because of the high water content.
Prior art references have chemically linked a hydrophilic polymer to a more durable undercoat to improve the physical integrity of the hydrophilic coating. See, Gould in U.S. Pat. No. 4,810,543 and Kliment in U.S. Pat. No. 4,729,914. Baker (U.S. Pat. No. 4,980,231) and Markel (U.S. Pat. No. 4,943,460) describe the coupling of a polyvinylpyrrolidone polymer with an undercoating of an acid functional or anhydride functional material.
The prior art also has attempted to improve wet strength and coating durability while retaining slip by physically blending or co-extruding the hydrophilic polymer with a co-material having greater physical integrity. See, Creasy in U.S. Pat. Nos. 4,642,267 and 4,847,324, in which a polyurethane or a polyvinyl butyral is blended with a poly(N-vinyl lactam). Other references disclose the preparation of interpolymers. See, Micklus (U.S. Pat. Nos. 4,100,309 and 4,119,094) which report an association between polyurethane and polyvinylpyrrolidone polymers. Whitborne in U.S. Pat. No. 5,001,009 describes hydrophilic coatings including a polyolefin such as polyvinylpyrrolidone and a water-insoluble stabilizing polymer, such as cellulose ester. The two polymers may be applied in separate layers or may be premixed and applied in a single step.
Other attempts in the prior art to improve the performance of hydrophilic coatings include use of modified polyurethanes, which possess short hydrophilic segments. See, Teffenhart in U.S. Pat. No. 4,789,720, in which a hydrophilic polyurethane is prepared having polyethylene glycol and polypropylene glycol segments. Stoy et al. in U.S. Pat. Nos. 4,370,451, 4,379,874, 4,420,589, 4,331,783, 4,369,294, 4,337,327 and 4,026,296 describe a series of hydrophilic block copolymers including acrylamides and modified acrylonitriles which have found some use as coatings. These polymers possess limited physical strength when hydrated and are delivered from organic solvents.
Elton in U.S. Pat. No. 5,077,352 describes a cross-linked polyurethane-poly(ethylene oxide) composition which is derived by polymerization of an isocyanate and a polyol in a poly(ethylene oxide) containing solution. The solvent used must not contain any active hydrogens and hence the system may not be applied from aqueous media.
Kiezulas in U.S. Pat. Nos. 5,026,607 and Opolski in 5,272,012 describe water-based, lubricous coatings having domains of a siloxane slip additive within a crosslinked urethane. The slip additives is maintained in distinct domains which replenish the surface of the slip additive as it is removed during use. While retaining good slip, the lubricous surface is non-robust and abrades easily due to the poor compatibility of the siloxane slip additive with the polyurethane and low crosslink density of the urethane. Further, there are health concerns with the retention of siloxane in the body.
In all the above examples, the coatings are either fragile and loosely bound to the substrate or demonstrate limited wet strength. In addition, most of the coating procedures require use of organic solvents, which is discouraged from environmental, cost and worker/patient safety standpoints. Thus, many technical problems directed to providing a durable, low-cost and safe hydrophilic coating remain unresolved.
It is an object of the present invention to provide a coating which is hydrophilic, containing water for anti-adhesion, slip and electrical and ion transport, yet durable--particularly in the water-swollen phase.
It is yet a further object of the invention to provide a coating which is a poor growth medium for microbes.
It is another object of the invention to provide a coating which may be applied from aqueous-based solutions.
These and other objects are provided by the present invention which is described hereinbelow.